In this study, silica xerogels are used as the cladding for high-refractive-index-contrast waveguide systems. Silicon oxide, due to its relatively low refractive index, is an extensively used cladding material. The lower-refractive-index silica xerogel films enable us, to report losses for planar-slab waveguide systems with silicon oxide as the core. A spin-on sol-gel process was used for the silica xerogel deposition. The silicon oxide core was deposited using plasma enhanced chemical vapor deposition (PECVD), with silane and nitrous oxide as the reactive gases. Slab waveguides systems with core thickness of 1 μm and refractive-index contrast (Δn) as high as 0.35 were fabricated. With regard to the PECVD process, a deposition temperature of 150 °C enabled a stable structure, however, unacceptably high optical losses of 7±1.01 dB/cm at a wavelength of 650 nm and 5.59±0.69 dB/cm at 830 nm were measured using a prism-coupler based setup. On increasing the deposition temperature of the silicon–oxide film to 225 °C, the losses decreased to 0.98±0.73 dB/cm at 650 nm and 0.69±0.46 dB/cm at 830 nm. The decrease in the losses resulting from increasing the deposition temperature provided the motivation to develop deposition conditions to reduce stress in the silicon–oxide films at higher deposition temperatures for improved stability on xerogel films. Reduction in the silicon–oxide film stress was achieved by varying the silane and nitrous oxide flow rates. The deposition stress in the film was reduced from ∼460 to ∼240 MPa, mainly by increasing the silane flow rate. The silicon oxide with the reduced stress was stable on xerogel film with porosities as high as 56%, even though a deposition temperature of 300 °C was used. However, the slab waveguide stack using the low-stress silicon oxide exhibited an optical loss of 1.81±0.18 dB/c m at 650 nm and 1.41±0.27 dB/cm at 830 nm. The higher loss, as compared to that obtained for the higher-stress film deposited at 225 °C, is attributed to scattering from the columnar structure of the lower-stress silicon–oxide film. © 2004 American Vacuum Society.